net: dsa: mv88e6xxx: use ports list to map bridge

Instead of digging into the other dsa_switch structures of the fabric
and relying too much on the dsa_to_port helper, use the new list
of switch fabric ports to remap the Port VLAN Map of local bridge
group members or remap the Port VLAN Table entry of external bridge
group members.

Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>